Although fires in buildings consume the fuel inside the building and may persist until the fuel is exhausted or the fire is extinguished by firefighters, the behaviour of a bush fire is different in that a fire front forms and travels over the ground according to various conditions which determine direction and speed.
Sometimes firefighting vehicles become isolated then surrounded by fire and the crew have no means of escape. Residences which are reached by only one road in a rural setting may become similarly surrounded by fire leaving the occupants trapped. The building codes do not yet specify that residences shall have fireproof construction. Accordingly some householders rely on bunkers into which they retreat in the event of a bush fire. Unless these are purpose-built they may provide inadequate protection and death or injury results.
The heat of a bush fire can be high over a short period as the fire front advances, consumes oxygen and creates smoke. Any refuge must therefore offer effective heat insulation, a physical barrier to smoke, windblown debris and embers, and an air supply in the event that the design limit of the refuge is exceeded by crowding.
In U.S. Pat. No. 4,174,711 is a fireproof shelter for installation inside a building. The shelter's wall is 12-20 cm thick with chrome plating or gold finish. Crystal hydrates inside the shelter absorb incoming heat and the occupants spray themselves with water. While it may be possible to use such shelters within buildings, the design of shelters for bush fire resistance and for mobile use on roads or across country requires a different approach.
In my Australian Patent No. 567145 I set forth a mobile refuge in the form of a water tank which is heat insulated sufficiently to withstand a moving fire front with hatches for rapid entry of persons who dump the water in the tank through a rapid discharge valve as they enter and remain inside for the duration of the emergency. The requirements of a dry refuge to which a family may retreat introduces different requirements from the tank version which are addressed by this invention.